Solution:Red tides is a phenomenon caused by Algal blooms during which algae become so abundant that they discolor coastal water (hence the name Red-tide). It is the overgrowth of microscopic algae or algae-like bacteria in fresh, salt, or brackish waters. Depending on the type of algae or bacteria that cause it, an algal bloom may produce bad-smelling scum, foam, froth, or a paint like slick. Algal blooms can be of many colors, including blue-green, yellow, brown, pink, and red. The growth and persistence of an algal bloom depends on wind direction and strength, temperature, nutrients, and salinity. It causes negative impact to other marine organism → lowers the Dissolved oxygen level in water → causes death of aquatic fauna and flora some Algae produces very harmful chemicals which ultimately led to death of many aquatic organisms.
Thus, the Correct answer is A.